1. Technical Field
The present invention relates generally to an in-line centrifugal fan, and in particular, to a centrifugal fan having a high operating efficiency and reduced sound.
2. Description of the Related Art
High performance fans are used in variety of industrial and laboratory applications to rapidly evacuate a large volume of air into, out of or through a building. The performance and desirability of a fan is measured generally by the fan's efficiency and sound levels produced during operation. The optimization of these two components will reduce the energy needed to operate the fan and/or increase output flow, thus conserving cost, and will further reduce the noise pollution associated with operation.
Fans are generally classified according to the direction of airflow through the impeller. In particular, axial flow fans are characterized by flow through the impeller in a direction generally parallel to the shaft axis. Centrifugal fans receive airflow into the impeller axially, and redirect the airflow radially outward. In-line mixed flow centrifugal fans are characterized in that the air enters the impeller axially and is deflected at an obtuse angle by the impeller blades such that the air flowing out of the impeller has both axial and radial flow components.
Centrifugal fans typically have a squirrel cage type impeller with multiple spaced apart fan blades that direct the air either radially, or both radially and axially. The fan blades are typically mounted to a wheel back that supports the fan blades as well as mounts to the shaft of a motor so that the impeller can rotate as the shaft is turned. The front end of the fan blades are mounted to a “wheel cone” that rotates with the impeller. The wheel cone cooperates with an inlet bell mounted in front of the impeller to funnel intake air into the impeller.
As disclosed in U.S. Pat. No. 7,048,499, the wheel back can be spherical and the wheel cone can be frusto-conical so as to mount the fan blades at an oblique angle with respect to the intake air flow to be better deliver the air to the fan blades. Specifically, by using specially designed fan blades, a conical wheel cone and angling the fan blades, the intake air can be distributed along most of the area of the fan blades, to thus output air flow efficiently.
This patent, and other prior art fan designs, focus on improving the impeller design through unique airfoil fins or twisted flat fin designs, rather than on improving how the air enters the wheel. However, the complex fan blades designs, convex wheel back and partial cone shape of the wheel cone complicates the fan design and manufacturing, and thereby increases cost, by requiring the fan blades to be formed with complex three-dimensional surfaces.
Accordingly, an improved centrifugal fan is need that improves fan efficiency and decreases noise without requiring a complex impeller configuration.